1. Field of the Invention
This invention relates in general to light curtain systems for detecting the movement or intrusion of objects into guarded zones. More particularly, the invention relates to light curtain systems which provide protection for human operators who are working with machines and other industrial equipment.
2. Description of the Related Art
Light curtains employing infrared beams are used to provide operator safety in a variety of industrial applications. Light curtains typically are employed for operator protection around machinery such as punch presses, brakes, molding machines, automatic assembly equipment, coil winding machinery, robot operation, casting operations and the like. The prior art light curtains typically employ light emitting diodes (LEDs) mounted at spaced positions along a transmitter bar at one side of the guard zone and phototransistors (PTs) mounted along a receiver bar at the opposite side of the zone. The LEDs transmit modulated infrared light beams along separate parallel channels to the PTs at the receiver bar. If one or more beam is blocked by penetration by an opaque object, such the operator's arm, the control circuit either shuts the machine down, prevents the machine from cycling or otherwise safeguards the area.
The typical existing light curtain system incorporates a control panel having a series of visible indicator lights. One of the lights is red for indicating that at least one of the beams is blocked so that the machine is prevented from cycling, and another light is green for indicating that no objects penetrate the guard area so that the machine can cycle. The control panel can also contain lights used for diagnostic purposes, such for indicating a power supply fault, for indicating receiver fault, for indicating transmitter fault or for indicating alignment. In the case where the machine cycling is interrupted by penetration of an opaque object, removal of the object causes the green indicator on the control panel to go on so that the operator can restart the cycle by pushing buttons or other controls provided outside the guard area.
For purposes of safety it is important that a condition should not arise in which the control panel shows the green indicator when it should show red, which would be an unsafe state. However, there are many possible failures that can arise in the machine and control circuitry which can cause such an unsafe state.
With the prior art light curtains the operator does not necessarily know what the real condition or problem is when the red light is observed on the control panel. Because the operator cannot see the invisible infrared beams, the presence of the red light on the panel would not tell him whether it was red because a beam was broken or whether some circuit or alignment problem caused it to go red.
When light curtain equipment is installed, replaced or re-aligned, a skilled technician is normally required to do the work. The alignment job is relatively difficult, especially where the transmitter and receiver bars are provided with lenses to form narrow beam angles. Because there is no feedback from the individual beams to the technician, it is difficult to adjust the transmitter and receiver bars until the single green light on the control panel comes on to indicate alignment.
The prior art includes light curtain systems having control panels with lights or other indicators related to individual beams for use by the technician in diagnosing and debugging problems, such as why the individual beam is not functioning. Such a system does not, however, provide feedback to the machine operator of the conditions in the guard area.